The redox characteristic of a mixed metal oxide catalyst is a key factor in controlling the activity and oxygenation function of the catalyst. These characteristics depend on the type of metal oxide mixed and their concentration. See, xe2x80x9cOxidative Dehydrogenation of Lower Alkane on Vanadium Based Catalystsxe2x80x9d, by E. Mamedov and V. Corberan, Applied Catalysis, vol. 217, pages 1-40 (1995). It would be desirable to derive a catalyst composition containing a specific combination of metal elements with suitable properties or characteristics to generate a redox characteristic catalyst having a significant impact on the selectivity and productivity of the oxygenation process. The mixed metal oxide catalysts of the present invention are prepared by an appropriate combination of the metal components, yielding a catalyst with a unique ability to selectively oxidize olefins to alpha-beta unsaturated aldehydes.
The present invention relates to the selective oxidation of hydrocarbons or olefins in the presence of molecular oxygen to form alpha-beta unsaturated aldehydes. This gas phase reaction is preferably carried out using a mixed metal oxide catalyst at temperatures in the range of 150xc2x0 C. to 450xc2x0 C. and at pressures of 1-50 bar. As a result, the method of the present invention achieves relatively high rates of selectivity and productivity.
The catalysts of the present invention are mixed metal oxides of the general formula
MoaPdbBicFedX1eX2fX3gOz,
wherein:
X1 is at least one element selected from the group consisting of Co, Ni, V, Pt, and Rh;
X2 is at least one element selected from the group consisting of Al, Ga, Ge, Mn, Nb, Zn, Ag, P, Si, and W;
X3 is at least one element selected from the group consisting of K, Mg, Rb, Ca, Sr, Ba, Na, and In;
a is 1;
b is 0 less than b less than 0.3, preferably 0.0000001 less than b less than 0.2;
c is 0 less than c less than 0.9, preferably 0.0001 less than c less than 0.5;
d is 0 less than d less than 0.9, preferably 0.0001 less than d less than 0.5;
e is 0 less than e less than 0.9, preferably 0.0001 less than e less than 0.5;
f is 0 less than f less than 0.9, preferably 0.0001 less than f less than 0.9;
g is 0 less than g less than 0.3, preferably 0.0000001 less than g less than 0.3; and
z is an integer representing the number of oxygen atoms required to satisfy the valency of the remaining components of the formula. The catalysts are preferably produced using the methods disclosed herein.
One aspect of the invention relates to a catalyst for the production of alpha-beta unsaturated aldehydes from olefins and hydrocarbons. According to one embodiment, the catalyst composition has the formula:
MoaPdbBicFedX1eX2fX3gOz,
wherein
X1 is at least one element selected from the group consisting of Co, Ni, V, Pt, and Rh;
X2 is at least one element selected from the group consisting of Al, Ga, Ge, Mn, Nb, Zn, Ag, P, Si, and W;
X3 is at least one element selected from the group consisting of K, Mg, Rb, Ca, Sr, Ba, Na, and In;
a is 1;
b is 0xe2x89xa6b less than 0.3, preferably 0.0000001 less than b less than 0.2;
c is 0xe2x89xa6c less than 0.9, preferably 0.0001 less than c less than 0.5;
d is 0xe2x89xa6d less than 0.9, preferably 0.0001 less than d less than 0.5;
e is 0xe2x89xa6e less than 0.9, preferably 0.0001 less than e less than 0.5;
f is 0xe2x89xa6f less than 0.9, preferably 0.0001 less than f less than 0.9;
g is 0xe2x89xa6g less than 0.3, preferably 0.0000001 less than g less than 0.3; and
z is an integer representing the number of oxygen atoms required to satisfy the valency of the remaining components of the formula.
According to a preferred embodiment of the invention, the catalyst composition has the general formula
MoaPdbBicFedX1eX2fX3gOz,
wherein:
X1 is at least one element selected from the group consisting of Co, Ni, V, Pt, and Rh;
X2 is at least one element selected from the group consisting of Al, Ga, Ge, Mn, Nb, Zn, Ag, P, Si, and W;
X3 is at least one element selected from the group consisting of K, Mg, Rb, Ca, Sr, Ba, Na, and In;
a is 1;
b is 0 less than b less than 0.3, preferably 0.0000001 less than b less than 0.2;
c is 0 less than c less than 0.9, preferably 0.0001 less than c less than 0.5;
d is 0 less than d less than 0.9, preferably 0.0001 less than d less than 0.5;
e is 0 less than e less than 0.9, preferably 0.0001 less than e less than 0.5;
f is 0 less than f less than 0.9, preferably 0.0001 less than f less than 0.9;
g is 0 less than g less than 0.3, preferably 0.0000001 less than g less than 0.3; and
z is an integer representing the number of oxygen atoms required to satisfy the valency of the remaining components of the formula. The catalysts are preferably produced using the methods disclosed herein.
Preferably, the catalyst is prepared from a solution of soluble compounds (salts, complexes, or other compounds) of each of the metals. The solution is preferably an aqueous system having a pH of 1 to 10, and more preferably at a pH of 1 to 7, and the solution is maintained at a temperature of about 30xc2x0 C. to about 100xc2x0 C. Water is removed by filtration to complete dryness, at which point the catalyst is dried in an oven at 100xc2x0 C. to 130xc2x0 C. for about 4 to about 24 hours. The dried catalyst is calcined by heating to about 250xc2x0 C. to about 600xc2x0 C., about 250xc2x0 C. to about 450xc2x0 C., in air or oxygen for about one hour to about 16 hours to produce the desired catalyst composition.
The catalyst may be used with or without a support. If desired, suitable supports include alumina, silica, titania, zirconia, zeolites, silicon carbide, molybdenum carbide, molecular sieves, microporous materials, nonporous materials and mixtures thereof. Support material can be pretreated with acids such as HCl, HNO3, H2SO4, per acids or heteroploy acids of phosphorous tungstate or silicotunstate, and alkali bases such as KOH or NaOH. When used on a support, the support usually comprises from about 50 to 95% by weight of the catalyst composition, with the remainder being the catalyst composition.
Preferably, molybdenum is introduced into the solution as an ammonium salt, such as ammonium paramolybdate, or as an organic acid salt of molybdenum, such as acetates, oxalates, mandelates, and glycolates. Some other partially water soluble molybdenum compounds which may be used in the present invention include molybdenum oxides, molybdic acid, and molybdenum chlorides.
Preferably, vanadium, bismuth, iron, cobalt, aluminum, gallium, silicon, germanium, antimony, phosphorous, niobium, potassium, magnesium palladium, tungsten, manganese are introduced as salts or acids, oxides, hydrate oxides, acetates, chlorides, nitrates, oxalates, or tartrates.
The method of the present invention is suitable for oxidation of hydrocarbons and olefins to alpha-beta unsaturated aldehydes. Preferably, the feedstock includes lower branched or straight-chained alkanes or alkenes, having C2-C6 carbon atoms. Further, the inventive catalyst can also be applied for the ammoxidation of C2-C5. In a preferred embodiment the starting material is propylene and acrolein is produced by the method.
The reaction mixture used in the method of the present invention is generally a gaseous mixture of 0.1 to 99 mol % olefins, such as propylene, 0.1 to 99 mol % molecular oxygen, either as pure oxygen or in the form of air, 0 to 50 mol % water, in the form of steam, and 0 to 90 mol % nitrogen or another inert gas. The gaseous mixture is generally introduced into the reaction zone at a temperature of about 150xc2x0 C. to about 500xc2x0 C., preferably from 250xc2x0 C. to 450xc2x0 C. The reaction zone generally has a pressure of from 1 to 50 bar, and preferably 1 to 30 bar. The contact time between the reaction mixture and the catalyst is preferably about 0.01 second to 100 seconds, and more preferably 0.1 second to 10 seconds, and the space hourly velocity is about 50 to about 50,000 hxe2x88x921, preferably about 100 to about 20,000 hxe2x88x921, and more preferably from 500 to 10,000 hxe2x88x921.
According to one preferred embodiment, the method comprises contacting a feed mixture comprising 1-50% by volume of olefins, 0.25 to 50% by volume oxygen or a gas capable of providing oxygen, 0-50% by volume steam and 10-80% by volume inert gas at a temperature of 170 to 450xc2x0 C. at a pressure of 15-500 psi at a space velocity of 500-20,000 hrxe2x88x921 with the catalyst. Preferably, the method provides a conversion greater than 90%, more preferably greater than 95%, most preferably greater than 98%, and a selectivity greater than 85%, more preferably greater than 90%, most preferably greater than 95%, of the olefins to the unsaturated aldehydes.
The process is generally carried out in a single stage in a fixed bed or fluidized bed or solid moving bed reactor with all the oxygen and reactants being supplied as a single feed and unreacted starting materials being recycled. However, multiple stage addition of oxygen to the reactor with intermediate hydrocarbon feed can be used. This may improve productivity and avoid a potentially hazardous condition.
The following examples are intended to be illustrative of this invention. They are, of course, not to be taken to in any way limit the scope of this invention. Numerous changes and modifications can be made with respect to the invention without departing from the spirit or scope of the present invention.